1. Field of the Invention
The present invention relates generally to the construction of dilation catheters for angioplastic treatment of obstructed blood vessels, and more particularly to an improved catheter construction wherein a sheath envelopes a flexible catheter tube to define both a dilation balloon at a distal end of the tube and an annular lumen connecting the balloon to a proximate end of the tube.
Balloon angioplasty was first described by Andreas Gruntzig in 1977. Dr. Gruntzig employed a balloon-tipped flexible catheter to percutaneously dilate a region of stenosis within the coronary artery of a patient with atherosclerotic coronary artery disease. Since the original work, the use of percutaneous balloon angioplasty has become widespread, with treatment of occluded peripheral blood vessels as well as coronary arteries.
A common type of dilation catheter consists of a pair of coaxial tubes which are sealed together at a distal end. The outer tube is expanded to form a balloon near a distal end of the catheter and a narrow annular lumen extends from the balloon to a proximate end. A fitting is secured to the proximate end, allowing for the infusion of an inflation medium through the annular lumen to the balloon. The catheter may be inserted over a guidewire to the desired location within a blood vessel, and inflated to dilate a stenosed region by now well known techniques.
The dilation catheter construction just described suffers from several drawbacks. In particular, the need to seal the outer tube to the inner catheter tube limits the choice of materials available for both tubes. For example, cross-linked polyolefins and halocarbon polymers, which are desirable as the material for the outer tube which defines the balloon, are difficult to bond to other materials suitable for the inner tube. Thus, most coaxial balloon catheters either avoid the use of such materials, compromise on the material used for the inner tube, or provide elaborate means for sealing the distal end. Second, even when compatible materials are chosen, the seam at the bonded end will be subject to failure when the catheter is use. Inflation pressures on the order of 80 to 260 psi are common, and bursting of the catheter could result in serious complications. Third, coaxial catheter constructions have typically included a rigid segment having a length on the order of 1 cm at the distal tip of the catheter. Such a rigid tip can, when the adjacent balloon is inflated, be pressed against the vessel wall. During the treatment of particularly tortuous vessels and/or with very high dilation pressures, the rigid tip can sometimes puncture the vessel wall. Finally, the construction methods employed in fabricating conventional dilation catheters are problematic and time consuming, increasing both the cost of production and the difficulty of meeting product specifications.
As an alternative to balloon angioplasty, various approaches have been proposed for the thermal ablation of vascular obstructions, including the use of direct laser radiation and heated contact elements. Although such techniques would be free from certain drawbacks of conventional balloon angioplasty, including restenosis and abrupt reclosure of the blood vessel, they suffer from their own disadvantages. Specifically, direct laser radiation can accidentally pierce the blood vessel wall, and it is often difficult to contact a heated element against the desired region of stenosis, particularly when the stenosis is non-uniformly distributed around the blood vessel.
Heating the inflation medium within balloons has been proposed as a method for remolding dissections which occur during conventional angioplasty, causing restenosis and abrupt reclosure. Heating for such remolding generally is carried out at lower temperatures than for ablation.
It would therefore be desirable to provide improved dilation catheters and methods for fabricating dilation catheters which do not require bonding between an inner tube and an outer tube, as described above, and which are free from rigid sealing segments at their distal ends. Moreover, it would be desirable that such methods allow for a wider selection of catheter materials and simplify the fabrication process to both reduce the cost of the process and provide for improved product quality. In particular, it would be desirable if such dilation catheters could be used in methods for the thermal ablation of vascular obstructions where the inflation medium within the balloon is heated to relatively high temperatures.
2. Description of the Background Art
The basic technique of balloon angioplasty is taught in U.S. Pat. No. 4,195,637. U.S. Pat. No. 4,323,071 and PCT Patent WO 87/00442 each describe the construction of coaxial balloon-tipped dilation catheters of the type described above. The use of direct laser energy for ablating stenosis is described in U.S. Pat. Nos. 4,445,892 and 4,448,188, and Sanborn et al. (1985) J. Am. Col. Cardiol. 5:934-938. Ablation of stenosis using a laser-heated metallic cap is described in Welch et al. (1987) Circulation 76:1353-1363, Sanborn et al. (1985) supra., and Lee et al. (1987) Am. Heart J. 113:1507-1508 and 114:1524-1526. The use of direct laser energy for the fusion of tissue dissected during balloon angioplasty is suggested in Spears (1987) Am. J. Cardiol. 61B-64B; Spears (1986) Cardiovasc. Intervent. Radiol. 9:303-312; and Hiehle, Jr., et al. (1985) Am. J. Cardiol. 56:953-957. U.S. Pat. No. 4,470,407 describes an endoscope which employs a laser-illuminated balloon. U.S. Pat. No. 4,754,752 describes a balloon catheter having a metal block heated by laser energy for convectively heating inflation medium within the balloon.